#ifndef _NTINTSAFE_H_INCLUDED_
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP | WINAPI_PARTITION_SYSTEM | WINAPI_PARTITION_GAMES)
//
// size_t multiplication
//
#ifdef _WIN64

#define RtlSizeTMult       RtlULongLongMult

#endif
#endif
#endif
View code on GitHub

#ifndef _NTINTSAFE_H_INCLUDED_
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP | WINAPI_PARTITION_SYSTEM | WINAPI_PARTITION_GAMES)
//
// size_t multiplication
//
#ifdef _WIN64
// ...
#else

_Must_inspect_result_
__inline
NTSTATUS
RtlSizeTMult(
    _In_ size_t Multiplicand,
    _In_ size_t Multiplier,
    _Out_ _Deref_out_range_(==, Multiplicand * Multiplier) size_t* pResult)
{
    ULONGLONG ull64Result = UInt32x32To64(Multiplicand, Multiplier);

    return RtlULongLongToSizeT(ull64Result, pResult);
}

#endif
#endif
#endif
View code on GitHub

// ntintsafe.h

NTSTATUS RtlSizeTMult(
  [in]  size_t Multiplicand,
  [in]  size_t Multiplier,
  [out] size_t *pResult
);
View the official Windows Driver Kit DDI reference

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Windows Driver Kit DDI reference (nf-ntintsafe-rtlsizetmult)

RtlSizeTMult function

Description

Multiplies one value of type SIZE_T by another.

Parameters

`Multiplicand` [in]

The value to be multiplied by Multiplier.

`Multiplier` [in]

The value by which to multiply Multiplicand.

`pResult` [out]

A pointer to the result. If the operation results in a value that overflows or underflows the capacity of the type, the function returns STATUS_INTEGER_OVERFLOW and this parameter is not valid.

Return value

Returns STATUS_SUCCESS if the operation is successful.

See the implementation of this helper function in ntintsafe.h in the WDK for possible error return values.

Remarks

This is one of a set of inline functions designed to provide arithmetic operations and perform validity checks with minimal impact on performance.

View the official Windows Driver Kit DDI reference